Hi guys,
If it's a bright, warm and sunny day you don't need a wetty, if it's one of those cold southerly winds, a wetty will make it a bit more comfortable. I only wear a 2mm shorty on the colder days but the water is OK at the moment, it's the wind chill that gets you.
You vico blokes should be HARD from all the freezing water and icy wind that you's get, so you'll probably sweat in a wetty over here.

Cheers,